1. FIELD OF THE INVENTION
This invention pertains to an edge connector for a printed circuit board. More particularly, this invention pertains to a make-before-break edge connector.
2. DESCRIPTION OF THE PRIOR ART
Make-before-break edge connectors for printed circuit boards are well known. An example of such is shown in U.S. Pat. No. 4,087,151 to Robert et al. dated May 2, 1978. As best illustrated in FIGS. 1-3 of the '151 patent, the make-before-break connector is a normally-closed electrical connector. Namely, electrical connection is made through the connector in the absence of an inserted circuit board (as shown in FIG. 1 of '151 patent). Upon partial insertion of printed circuit board into the connector, the connector first makes electrical connection with the printed circuit board before breaking the normal through electrical connection in the connector. The make-before-break position is shown in FIG. 2 of the '151 patent with the circuit made to the printed circuit board before being broken through the connector. FIG. 3 of the '151 patent shows full insertion of printed circuit board into a connector with the circuit made through the connector and broken through the connector.
Additional make-before-break connectors are shown in U.S. Pat. Nos. 4,286,121 and 4,106,841, and UK Patent Application GB 2133938A. A make-before-break connector (referred to as a "shorting edge connector") is also shown in U.S. Pat. No. 4,514,030 dated Apr. 30, 1985 to Triner et al. In the '030 patent, two opposing spring contacts 28,30 include normally closed contact ends 40,40' and normally closed contact portions 46,46'. Between contact portion pairs 40,40' and 46,46' is a spacing 42,42'. The spacing is slightly smaller than the thickness of an edge of a printed circuit board to be inserted into the connector. FIGS. 4A-4C of the '030 patent illustrate the make-before-break operation of the connector. FIG. 4A shows the connector in an absence of a printed circuit board. In this state, electrical connection is made between contacting pairs 46,46' and 40,40'. Upon partial insertion of a printed circuit board (as shown in FIG. 4B of '030 patent), the printed circuit board passes between pairs 40,40' resulting in electrical contact (i.e. a "making" of a circuit) with electrical contacts (not shown) on the printed circuit board. Further insertion of the printed circuit board into the contact results in the printed circuit board increasing the separation between surfaces 42,42' (as shown in FIG. 4C of the '030 patent). This increase in separation results in separation of the contacts 46,46'. Hence, the normal through circuit through the connector is now broken with the only connection being made through the printed circuit board and any circuit which might happen to be contained on the printed circuit board.
There is a continuing need for development of improved make-before-break connectors notwithstanding the current state of the art. Such connectors should have high reliability to prevent premature breaking of the circuit through the connector. For example, with reference to U.S. Pat. No. 4,514,030, the connector is commonly contained within a housing 10 of insulated' material such as plastic and the like. With the structure as shown in the '030 patent, a single contact point of each connector (in the vicinity of bends 38,38') bears against the walls of the housing 10. As a result, due to the resiliency of the spring contacts of the connector, a force is constantly being applied to an isolated location on the plastic walls. In response to the continued presence of such a force, the plastic material may creep or otherwise plastically deform resulting in movement of the spring contacts into the wall. The plastic deformation and creep is particularly heightened during high temperature applications. If this were to occur, the contact portions 46,46' may prematurely separate resulting in an undesired break of the circuit through the connector. Also, the close touching proximity portions 40,40' in the '030 patent, results in a required large displacement of the bends 40,40' upon insertion of a printed circuit board. Namely, the portions 40,40' must each be deflected about half the complete thickness of the printed circuit board. The greater the deflection required, the greater the force applied against the plastic housing 10 which increases the possibility of plastic deformation. Further, the increased displacement results in increased stresses on the bend portions 38,38' which increases the probability of failure of the springs.
It is an object of the present invention to provide an improved make-before-break connector.